Too Much Caffeine Raises Risk of Miscarriage

Action Points

Explain to interested patients that the study supports elevated risk of miscarriage with high intake of caffeine during pregnancy.

Caution patients that this study found that even small amounts of caffeine were associated with a modest but not statistically significant increase in miscarriage risk.

OAKLAND, Calif., Jan. 21 -- Caffeine's dangers in pregnancy are real, and it may be prudent to halt or reduce the intake of caffeinated beverages to lessen the risk of a miscarriage, according to a large prospective cohort study here.

Pregnant women who drank the equivalent of at least two cups of coffee daily, or five cans of a soft drink with caffeine, were twice as likely to miscarry as women who consumed no caffeine, found results of the study reported online in the American Journal of Obstetrics & Gynecology.

Lower caffeine intake was also associated with a 42% increased risk of unintentional termination of pregnancy by 20 weeks gestation compared with no caffeine, although the difference was not significant, wrote De-Kun Li, M.D., Ph.D., of Kaiser Permanente here, and colleagues.

The study controlled for the confounding effects of nausea and vomiting during pregnancy.

Other studies have also reported increased risk of miscarriage with caffeine, which crosses the placenta but is poorly metabolized by the fetus and may influence cell development and decrease placental blood flow.

However, critics have argued that the association arose not from a true effect but rather that women with a healthy pregnancy were more likely to cut back on caffeine because of nausea and vomiting, the researchers said, "which are generally associated with a low risk of miscarriage."

The study removed those doubts, Dr. Li concluded, and strengthened the recommendation for women to avoid caffeine in pregnancy.

"It may be prudent to stop or reduce caffeine intake during pregnancy," he and colleagues wrote.

Their study included 1,063 women in the San Francisco area who were members of the Kaiser Permanente integrated health care system. The women became pregnant from October 1996 through October 1998.

Soon after each woman's pregnancy was confirmed with laboratory tests, a person-to-person interview was conducted to evaluate her exposure since her last menstrual period to caffeine from regular or decaffeinated coffee or tea, caffeinated soft drinks, and hot chocolate.

The researchers estimated that every 150 mL of regular coffee contained 100 mg of caffeine, while the caffeine in a similar volume was estimated at 2 mg for decaffeinated coffee and hot chocolate and 39 mg for caffeinated tea.

A quarter of women reported no caffeine consumption whatsoever in pregnancy, whereas 60% reported up to 200 mg of caffeine per day and 15% reported higher daily intake.

Those with a moderate daily intake of caffeinated drinks were more likely to miscarry than those who went without (15.30% versus 12.50%), but the difference was not significant (adjusted hazard ratio: 1.42, 95% confidence interval: 0.93 to 2.15).

The risk was substantially greater, though, among women who reported more than 200 mg of caffeine per day (25.45% versus 12.50%) and remained essentially unchanged after adjustment for factors including prior miscarriage and nausea and vomiting (HR: 2.23, 95% CI: 1.34 to 3.69).

This dose response to caffeine was significant (P<0.01), and the associations remained regardless of source.

Although 79% of women cut down on caffeinated beverages after they became pregnant, those who continued to take in at least 200 mg caffeine tended to remain at elevated risk of miscarriage (HR: 1.31, 95% CI: 0.73 to 2.37).

Women with nausea had a somewhat higher risk of miscarriage associated with high caffeine intake than women without the symptom, but both groups had elevated risk (HR: 2.02 and 1.57, respectively).

The researchers acknowledged that their estimations of caffeine intake may not have accurately reflected content in the specific brands or with the brewing methods used by the women.

The study may have been subject to recall bias because some participants were interviewed soon after their miscarriage or to selection bias because of low participation rates, Dr. Li and colleagues said.

This study was supported in part by the California Public Health Foundation. The researchers provided no information on conflicts of interest.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco

Accessibility Statement

At MedPage Today, we are committed to ensuring that individuals with disabilities can access all of the content offered by MedPage Today through our website and other properties. If you are having trouble accessing www.medpagetoday.com, MedPageToday's mobile apps, please email legal@ziffdavis.com for assistance. Please put "ADA Inquiry" in the subject line of your email.